Three Egyptians, including two with British citizenship, have been released by Cairo police after being held in a probe into sabotage plot claims.

A man told police he overheard them discussing ways to destabilise the country during next month's anniversary of the 2011 uprising, a security official and a British diplomat said.

A brother, his sister and their cousin were arrested at a subway station on Saturday after a passenger told police they were speaking in English about burning homes and businesses on the anniversary of the uprising which led to the ousting of Hosni Mubarak.

The three denied the accusations and the case was referred to prosecutors.

A British diplomat said the British nationals were provided consular assistance and were subsequently released.

The British Embassy in Cairo has been closed to the public since last week because of security fears.

Since the 2011 uprising, successive governments have stoked fear of foreigners, warning the public that a myriad of "foreign hands" have been behind attempts to destabilise the country. At one point in 2012, a public service announcement was played on national television warning Egyptians against talking to foreigners, including in public places, for fear they would be spies.

This has increased citizen accusations against unsuspecting foreigners, including one that led to the brief detention of a prominent French journalist last month who was speaking to two Egyptians in a Cairo coffee shop. A woman in the cafe screamed after hearing their conversation in English and Arabic and reported them to the security forces nearby.